1. Field of the Invention
This invention relates to a light emitting device capable of changing an illumination range and a camera having the same.
2. Description of the Related Art
Conventionally, a variety of illuminating devices for use in a photographing apparatus such as a camera have been proposed in order to efficiently converge luminous fluxes, which are emitted from a light source in various directions, within a required illumination angle of view.
Particularly in recent years, the convergence efficiency have been improved and the size of a photographing apparatus has been reduced by providing an optical member that performs total reflection on a prism, a light guide, and the like in place of a Fresnel lens, which is conventionally disposed in front of a light source.
In recent years, a photographing apparatus such as a camera has been reduced in size and weight whereas the zooming magnification of a taking lens has been increasing. Generally, a full aperture f-number of the taking lens tends to gradually increase with the reduction in size of the photographing apparatus and the increase in the magnification. If a picture is taken without using an auxiliary light source, an image on the picture is unexpectedly blurred due to the motion of the photographer's hand or the motion of a subject, or a failed picture is produced due to underexposure. To address this problem, an illuminating device serving as an auxiliary light source is usually built in the photographing apparatus.
Under the circumstances, the frequency with which the illuminating device is used is increased to a large extent, and the quantity of emitted light required for one photography is increased. Thus, the illumination range is usually fixed correspondingly to the wide-angle photography, and an undesired range is illuminated in the telephotography. It is therefore disadvantageous to use an illuminating device with a fixed wide illumination range since a large amount of energy is lost.
Accordingly, a variety of illuminating devices have been proposed which are capable of changing the illumination range so as to illuminate only a range corresponding to a shooting angle of view to thus save power. In particular, some illuminating devices have been proposed which improve the luminous efficiency by total reflection.
For example, an illuminating device proposed in Japanese Laid-Open Patent Publication No. 4-138439 (Kokai) by the assignee of the present invention has a convergent optical system arranged at a front portion of the illuminating device and comprised of an optical prism having two upper and lower entrance surfaces having a positive refracting power and which luminous fluxes emitted mainly from a light source laterally with respect to an exit optical axis enter, two upper and lower total reflection surfaces upon which the luminous fluxes are totally reflected, and exit surfaces through which the totally reflected fluxes are emitted toward a subject. In this convergent optical system, the positions of the optical prism and the light source are relatively changed to cause the luminous fluxes to be reflected by or transmitted through the total reflection surfaces to thereby change the illumination range.
In an illuminating device proposed in Japanese Laid-Open Patent Publication (Kokai) No. 8-262538, an optical prism is divided into a plurality of parts, and the optical prism disposed vertically is rotated to change the illumination range.
However, the illuminating devices disclosed in the above publications provide a relatively easy convergence and diffusion control of directing the luminous fluxes in a diametrical direction of a cylindrical discharge arc tube as the light source, i.e. in a direction (vertical direction) orthogonal to the longitudinal direction of the light source (transverse direction with respect to the axis of illumination light), but do not provide a convergence diffusion control of directing the luminous fluxes in the longitudinal direction of the light source (transverse direction with respect to the axis of illumination light). Therefore, the illumination range cannot always be controlled in an ideal manner because the illumination range can be controlled only in the longitudinal direction.